Problems with fogging have plagued the photographic industry from its inception. Fog is a deposit of silver or dye that is not directly related to the image-forming exposure, i.e., when a developer acts upon an emulsion layer, some reduced silver is formed in areas that have not been exposed to light. Fog can be defined as a developed density that is not associated with the action of the image-forming exposure, and is usually expressed as "D-min", the density obtained in the unexposed portions of the emulsion. Density, as normally measured, includes both that produced by fog and that produced as a function of exposure to light. It is known in the art that the appearance of photographic fog related to intentional or unintentional reduction of silver ion (reduction sensitization) can occur during many stages of preparation of the photographic element including silver halide emulsion preparation, spectral/chemical sensitization of the silver halide emulsion, melting and holding of the liquid silver halide emulsion melts, subsequent coating of silver halide emulsions, and prolonged natural and artificial aging of coated silver halide emulsions. The chemicals used for preventing fog growth as a result of aging or storage are generally known as emulsion stabilizers.
The control of fog, whether occurring during the formation of the light-sensitive silver halide emulsion, during the spectral/chemical sensitization of those emulsions, during the preparation of silver halide compositions prior to coating on an appropriate support, or during the aging of such coated silver halide compositions, has been attempted by a variety of means. Mercury-containing compounds, such as those described in U.S. Pat. Nos. 2,728,663; 2,728,664; and 2,728,665, have been used as additives to control fog. Thiosulfonates and thiosulfonate esters, such as those described in U.S. Pat. Nos. 2,440,206; 2,934,198; 3,047,393; and 4,960,689, have also been employed. Organic dichalcogenides, for example, the disulfide compounds described in U.S. Pat. Nos. 1,962,133; 2,465,149; 2,756,145; 2,935,404; 3,184,313; 3, 318,701; 3,409,437; 3,447,925; 4,243,748; 4,463,082; and 4,788,132 have been used not only to prevent formation of fog but also as desensitizers and as agents in processing baths and as additives in diffusion transfer systems. Organic compounds having a polysulfur linkage comprised of three or more sulfur atoms, and organic compounds having a heterocyclic ring having at least two thioether linkages or at least one disulfur linkage, such as those described in U.S. Pat. No. 5,116,723, in combination with nitrogen-containing cyclic compounds have also been discussed as suppressing fog and improving raw stock stability.
Recently, a class of compounds has been reported to have benefits in stabilizing silver halide emulsions against such changes due to storage at high temperature and humidity. This class of sulfur heterocycle are compounds in which one of the two sulfur atoms in a five-membered heterocyclic ring is oxidized either to the tetravalent state (dithiolone dioxide) or to the trivalent state (dithiolone oxide). U.S. Pat. No. 5,693,460 teaches the stabilizing properties of dithiol-3-one 1,1-dioxides. U.S. Pat. No. 5,670,307 describes the combination of dithiol-3-one 1,1-dioxides with sulfinates. U.S. Pat. No. 5,756,278 relates to the combination of water soluble gold sensitizers with dithiolone dioxide compounds for enhanced emulsion sensitivity. U.S. Pat. No. 5,677,119 describes the stabilizing properties of dithiol-3-one 1-oxide in silver halide light sensitive materials.
Another type of fogging may also occur in a photographic element. When pressure is applied to a silver halide photographic print during wet processing it may cause an unwanted plus or minus density mark in the exposed region of the color print. This problem is known as Wet Abrasion Sensitivity (WAS) and is particularly acute for the magenta layer of the photographic element. The problem may be exacerbated when certain mercapto azole compounds are used as addenda in the photographic element. Removal of the mercapto azole compounds has been suggested as a method to minimize WAS; but mercapto azoles provide a variety of benefits such as the minimization of "magenta dye streaking", antifogging, emulsion stabilizing and development modifying and it is therefore desirable to continue using these compounds. Such compounds are well known in the art and examples of their use are given in "Stabilization of Photographic Silver Halide Emulsions" by E. J. Birr Focal Press, London and New York 1974. Generally mercapto azole compounds are added as addenda after chemical sensitization is complete.
U.S. Pat. No. 4,962,016 describes a photographic element which has high sensitivity and excellent pressure resistance. This is achieved by utilizing a photographic component layer with a certain degree of swelling and which contains elemental sulfur. The photographic element may also contain certain mercaptoazoles, which are preferably added during the coating solution preparing step. It has been discovered by the inventors herein, however, that the addition of mercapto azole compounds solely after chemical sensitization results in poor WAS performance.
There is a continuing need for photographic elements that are not prone to the WAS that causes deterioration of the print by pressure applied during development. There is a further need for the correction of this problem without generating speed losses in the photographic element or creating stability problems either in the melts prior to the formation of the photographic element or in the photographic element during storage prior to exposure.